The Universal Mobile Telecommunication System (UMTS) is one of the third generation mobile communication technologies designed to succeed the Global System for Mobile communications (GSM). Long Term Evolution (LTE) is a project within the 3rd Generation Partnership Project (3GPP) to improve the UMTS standard to cope with future requirements in terms of improved services such as higher data rates, improved efficiency, and lowered costs. The Universal Terrestrial Radio Access Network (UTRAN) is the radio access network of a UMTS and Evolved UTRAN (E-UTRAN) is the radio access network of an LTE system. In an E-UTRAN, a wireless device such as a User Equipment (UE) 150 is wirelessly connected to a base station (BS) 110a commonly referred to as an evolved NodeB (eNodeB), as illustrated in FIG. 1. In E-UTRAN, the eNodeBs 110a-c are directly connected to a core network (CN) 190.
The LTE Rel-8 standard has been standardized, supporting bandwidths up to 20 MHz. However, in order to meet the International Mobile Telecommunications (IMT) advanced requirements, 3GPP has initiated work on LTE Rel-10. One of the parts of LTE Rel-10 is to support bandwidths larger than 20 MHz. One important requirement on LTE Rel-10 is to assure backward compatibility with LTE Rel-8. This should also include spectrum compatibility. That would imply that an LTE Rel-10 carrier, wider than 20 MHz, should appear as a number of LTE carriers to an LTE Rel-8 terminal or UE. Each such carrier can be referred to as a component carrier or a cell. In particular for early LTE Rel-10 deployments it can be expected that there will be a smaller number of LTE Rel-10-capable UEs compared to many LTE legacy UEs, i.e. UEs of earlier LTE releases. Therefore, it is necessary to assure an efficient use of a wide carrier also for legacy UEs, i.e. that it is possible to implement carriers where legacy UEs can be scheduled in all parts of the wideband LTE Rel-10 carrier. The straightforward way to obtain this would be by means of carrier aggregation, which is schematically illustrated in FIG. 2, where five component carriers or cells 210, each of 20 MHz bandwidth, have been aggregated together to form an aggregated bandwidth of 100 MHz. Carrier aggregation implies that an LTE Rel-10 UE can receive or transmit on multiple component carriers or cells, where the component carriers could have, or at least have the possibility to have, the same structure as a Rel-8 carrier.
LTE uses Hybrid Automatic Repeat Request (HARQ). After receiving downlink data in a sub frame, the UE attempts to decode it and reports to the eNodeB whether the decoding was successful or not. The acknowledgment is sent in the form of an ACK when decoding is successful, and in the form of a NACK when the decoding is unsuccessful. In case of an unsuccessful decoding attempt, the eNodeB may retransmit the data that was unsuccessfully decoded.
Uplink control signaling from the UE to the eNodeB comprises, in addition to HARQ acknowledgements for received downlink data:                Scheduling requests, indicating that a UE needs uplink resources for uplink data transmissions; and        Reporting of information related to the downlink channel conditions, typically referred to as Channel Status Information (CSI) reporting, used as assistance for the eNodeB downlink scheduling. Such CSI reports may comprise Channel Quality Indicators (CQI), Precoding Matrix Indicators (PMI) and Rank Indicators (RI).        
The uplink control information is transmitted in uplink resources specifically assigned for uplink control on a Physical Uplink Control Channel (PUCCH), if the UE has not already been assigned an uplink resource for data transmission. On the other hand, if the mobile terminal or UE has been assigned an uplink resource for data transmission and at the same time instance has control information to transmit, the UE will typically transmit the control information together with the data on the Uplink Shared Channel (UL-SCH). FIG. 3 illustrates schematically the position of data and the different control information types in one uplink sub frame from one UE, when using normal cyclic prefix. As illustrated in FIG. 3, CQI and PMI are jointly coded and use the same set of resource elements. Scheduling requests are not transmitted together with uplink data. Instead a buffer status report is transmitted jointly coded with the data if such a status report has been triggered. CQI/PMI may be requested by bits in the uplink grant. The CQI/PMI format used for requested reports is often frequency selective, while periodic reports configured on PUCCH is smaller but often non-frequency selective.
The different control types are differently multiplexed with data. The amount of resources used for CQI/PMI and RI is taken into account when data is placed in the sub frame, so that data is only placed at the positions not allocated by CQI/PMI and RI. The HARQ ACK/NACK then overwrites the data and possibly also CQI/PMI.
The amount of data that is transmitted within assigned resource blocks in uplink is indicated by the number of resource blocks assigned and a Modulation and Coding Scheme (MCS), based on a MCS table 40 as illustrated in FIG. 4. Each point of the table indicates the transport block size for a certain combination of the number of scheduled resources and the modulation and coding scheme. Quadrature phase-shift keying (QPSK) modulation, 16 Quadrature Amplitude Modulation (16QAM), and 64QAM may be used in LTE for UL-SCH transmission. Transport block sizes, such as the ones corresponding e.g. to the points 41, 42 and 43 indicated in the enlarged circle, may be the same although they correspond to different numbers of resource blocks. One of the principles behind this design is that the amount of resource blocks assigned to the uplink transmission should be independent from the set of possible code rates, i.e. the same code rates for data is available independently from the number of resource blocks assigned.
The amount of control information that is transmitted together with data is determined by the code rate of data, without taking the amount of control information into account. Since the data on Physical Uplink Shared Channel (PUSCH) is protected by the HARQ protocol, it is usually operated at a higher error rate than the error rate required for the HARQ ACK/NAK, CQI/PMI and RI. Therefore it is since LTE Rel-8 possible to configure an offset so that control information is given a lower code rate than data by a certain number of dBs. This offset is referred to as the Beta offset. The exact principle of how to use the Beta offset is defined in section 5.2.2.6 of the 3GPP TS 36.212, v.10.0.0, and in section 8.6.3 of the 3GPP TS 36.213, v.10.0.1.
It is possible to send reports regarding the downlink channel condition on PUSCH also without data, indicated by a special point in the MCS table. No Beta offset is used in this case. If other control information is multiplexed with such a transmission the code rate of that control information is dependent on the code rate of CQI/PMI instead of on the code rate of data.
The CQI/PMI is encoded with the Reed-Muller (RM) encoder if the number of information bits is below twelve. If the number of information bits is above eleven, the CQI/PMI is encoded with the tail-biting convolutional code instead.
If the UE aggregates several downlink cells, it can transmit an aperiodic CSI report for several downlink cells. The CSI reports will only be transmitted on a single uplink component carrier. In case one or more aperiodic CSI report is transmitted, all the reports will be transmitted on PUSCH. They can then be multiplexed together with data or they can be sent on a PUSCH transmission without data as described previously.
The eNodeB may trigger the UE to report aperiodic CSI reports by using a two bit trigger in the uplink grant. In Rel-10 this triggering mechanism has been extended so that it includes a possibility to trigger an aperiodic CSI report for the serving cell, an aperiodic CSI report for each of a first set of serving cells configured by higher layers, and an aperiodic CSI report for each of a second set of serving cells configured by higher layers, instead of only triggering an aperiodic CSI for the corresponding downlink (DL) cell. In total there are thus three possible aperiodic CSI report triggering options. The two cell sets for aperiodic CSI report triggering may include all from one to all configured downlink cells. However, the actual reporting is limited to the activated cells in the set. A detailed description of the triggering of aperiodic CSI reports is available in section 7.2.1 of the 3GPP TS 36.213, v.10.0.1.
For Rel-10 the CQI/PMI reporting payload will grow in size, since it will be possible to report aperiodic CSI reports for all activated component carriers or cells on a single PUSCH transmission. In Rel-8/9 the aperiodic CSI, which may comprise up to 72 bits payload, is coded with a convolutional code. However, for larger CQI/PMI payload sizes, the convolutional coding may not be so efficient. Furthermore, it is possible for the eNodeB to change between triggering aperiodic CSI for many downlink cells and triggering for only a single downlink cell on a sub frame basis, so the CQI/PMI payload size will vary from sub frame to sub frame. There is therefore a need for improving CQI/PMI transmission when the CQI/PMI payload sizes increase.